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Hurricane Miriam Discussion Number  16
NWS Central Pacific Hurricane Center Honolulu HI   EP152018
500 PM HST Wed Aug 29 2018
 
While cloud tops associated with Miriam were on general warming 
trend since the previous advisory, a new burst of convection has 
recently developed over the center, while organized convective
bands continue to wrap in to the center from the southeast.
Subjective Dvorak intensity estimates of 4.0/65 kt from SAB/HFO are
supported by UW-CIMSS ADT, and that will be the initial intensity
estimate for this advisory. 

The initial motion estimate is a somewhat uncertain 280/7 kt, as
the low-level center has been difficult to identify. Miriam has
moved into an area of light steering flow between a mid-level ridge 
centered over the southwestern U.S., and a mid- to upper-level low 
centered northeast of Hawaii. The gradient between the low and the 
ridge will result in a southerly steering flow that will take
Miriam toward the north the next couple of days. A turn toward the 
northwest is expected to begin tonight, followed by a turn toward 
the north on Thursday, with the dynamical models in good agreement 
on this evolution. Increasing model spread persists after day 3, 
with ECMWF taking a deeper cyclone much faster and farther
northward than the most of the guidance, with this solution taking
consensus members well to the right of the updated forecast track.
The official forecast continues to lean toward the GFS and its
ensemble solution, with Miriam turning west-northwestward toward the
end of the forecast period as a weak and shallow system primarily
steered by the low-level trade wind flow. 

The forecast anticipates that Miriam will be in an environment 
conducive for modest strengthening for the next 24 hours or so,
with shear near 10 kt and SSTs near 28C. The forecast track toward
the north will take Miriam over cooler waters thereafter, with SSTs 
below 26C by 72 h. Southwesterly shear is expected to increase to 
near 30 kt in 48 h and to 40 kt in 72 h, and Miriam is expected to 
degenerate into a remnant low by day 4. The official intensity 
forecast follows trends presented by the multi-model consensus and 
SHIPS.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  30/0300Z 14.4N 140.6W   65 KT  75 MPH
 12H  30/1200Z 14.8N 141.2W   70 KT  80 MPH
 24H  31/0000Z 16.0N 141.6W   75 KT  85 MPH
 36H  31/1200Z 17.7N 141.5W   65 KT  75 MPH
 48H  01/0000Z 19.4N 141.6W   55 KT  65 MPH
 72H  02/0000Z 22.0N 143.2W   40 KT  45 MPH
 96H  03/0000Z 25.0N 147.0W   30 KT  35 MPH...POST-TROP/REMNT LOW
120H  04/0000Z 27.0N 151.5W   25 KT  30 MPH...POST-TROP/REMNT LOW
 
$$
Forecaster Birchard
 
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